


The Clave's Mischief

by rei_c



Series: Mashups and Crossovers [4]
Category: Teen Wolf (TV), The Mortal Instruments Series - Cassandra Clare
Genre: Age Swap, Alternate Universe, Crossovers & Fandom Fusions, M/M, Mating Bites, Mating Bond, Scents & Smells, Underage Derek Hale
Language: English
Status: Completed
Published: 2019-09-19
Updated: 2019-09-19
Packaged: 2020-10-21 21:11:01
Rating: Mature
Warnings: Underage
Chapters: 1
Words: 2,480
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20699918
Author URL: https://archiveofourown.org/users/rei_c/pseuds/rei_c
Summary: Derek's not expecting to meet his mateever, much less on a random day of the week while he's trying to make sense of his math homework.





	The Clave's Mischief

**Author's Note:**

> A few different things going on here: Shadowhunter!Stiles, age swap where Stiles is in his mid-20s and Derek's still in high school, no mentions of Paige or Kate, but Peter's still -- y'know, Peter.
> 
> (Also, in this universe, the Argents used to be, centuries ago, Shadowhunters as well, but were excommunicated as a line.)
> 
> (... Don't ask me about Stiles' family. I have backstory and it's tragic.)

Derek's the only one downstairs when the doorbell rings, so he gets up from the kitchen table and his homework. He can hear footsteps upstairs -- his mother, it sounds like, and someone else, probably Uncle Peter -- as he makes his way to the front door, so even though he doesn't recognise the rhythm of the heartbeat standing outside, he's not too worried. The _thu-thump_ is fast but steady, deeper than he'd expect from such a galloping pace, and Derek assumes he's going to open the door to see an older human, maybe someone his mother works with or his uncle knows from his summer internship working in the mayor's office. 

The face he sees is not at all what he was expecting. The man standing on the porch is tall, taller than Derek by a good handful of inches, with amber-brown eyes barely darker than a beta's in shift. Dark messy hair that curls over his ears, pale skin, dressed like an off-duty soldier who still prefers the feel of a uniform -- tight, long-sleeved black shirt, black combat pants tucked into boots -- and the _weapons_, jesus. The guy's got two swords crossed on his back, throwing knives strapped to each bicep, longer daggers on thigh holsters, and something wrapped to his left forearm that looks like a ceremonial -- pen? 

Faced with all of that, it takes Derek a couple of long, slow blinks and staring to notice the edge of tattoos curling up the guy's neck, covering the back of his hands. 

Just -- _shit_. 

"Greetings of peace and blessing," the guy says. His voice sounds like silk rubbing up against Derek's skin, twisting and coiling around him. Derek gets chills, hearing it; his wolf pants, sinking to its belly. "I was hoping to speak with Alpha Hale, if she's available?" 

Thank god Derek feels his mother approach, put her hand on his shoulder, because there's no way he can say _anything_ to this guy. It's like all of his higher brain functions have melted into goo the way his bones want to. 

"Stiles," Talia says. "The Hale pack is honoured by a visit from the Clave's Mischief. How can we be of service?" 

The guy -- Stiles dips his head, lets his eyes go down to the ground before they rise and focus on Talia's face, though his head tilts, just enough to show off the curve of his neck. Derek wants to plant his face there and _bite_. "I'm here to pass along a message from the Clave," he says, "and to ask for your help. There's a group of 'wolves up in Seattle that I've been sent to visit; I thought you might like to send someone along to impress upon them the need for cooperation?" 

Talia's scent fills with curiosity and interested agreement. It hits Derek, then, that he can't smell Stiles. "Let's go to my office," she says, and invites Stiles inside. "Something to eat or drink? How long has it been since your last meal?"

Stiles grins, says, "Not that long, Alpha Hale. I'm fine, thank you." 

The two of them head upstairs to Talia's office. Derek feels helpless to do anything but watch them go. 

\--

By the time Derek's gathered himself, closed the front door, and gone back to the kitchen to try and focus on homework when all he can do is think about how those pants hugged the curves of Stiles' hips and ass, Peter's got a glass of water in one hand and his eyes fixed on the ceiling as if he's watching the meeting. 

"Who is that?" Derek asks. "Stiles? Is he a hunter?" 

"Shadowhunter," Peter says, half-agreement and half-correction. "What hunters wish they were. Or used to be." 

Derek shakes his head, frowning. "I've never heard of Shadowhunters before." 

Peter sips his water, finally takes his eyes off of the ceiling and pins them on Derek. "And for good reason," he says. "Shadowhunters are -- legend. How my sister and Stiles ever became -- friends might be pushing it, but definitely allies at the _least_ \-- I'll never know. Something to do with the war, I think." Peter's eyes narrow, then, and he asks, "Why so interested?" 

"I couldn't smell him," Derek says. "Couldn't scent anything off of him. But -- there's something -- I dunno." 

"Forget it," Peter says, sharply. "For all the goodwill Stiles has towards Downworlders, his people don't. And he's in a precarious enough position with the Clave already."

Derek's wolf whines inside of him, in refusal and want and worry, all at the same time. "Is he in trouble?" 

Peter holds Derek's gaze, then snorts. "Ask your mother to explain it," he says. He sets down his glass with a thump, leans forward, hands on the table. His eyes flare blue, claws come out to tap gently on the wood. "Leave him alone, Derek. Leave everything about him alone." 

Derek snarls, his own claws coming out. He can feel the pinpoint pressure of his fangs descending, can feel the heat behind his eyes that mean they've changed colour, and he stands as well, faces Peter down. "_No_," he says, growl edging his word, riding along the bottom of his breath. "Never." 

There's a long, tense moment where Derek doesn't know if Peter's going to leap across the table or if _he_ is, but it's broken when Peter leans back, all signs of his wolf pushed away, and says, "Be it on your own head, then, nephew," before sauntering towards the stairs. 

It takes Derek much, much longer to calm himself down. 

\--

He's finally started tackling his math again when movement upstairs catches his attention. He strains to listen for more behind the creaking floorboards, but nothing comes until someone opens the door to his mother's office. 

"-- contact with you as soon as they arrive," Talia's saying. "You still have the same number?" 

"Fifth phone, same number," Stiles says. "Thank god for technology ports and back-ups. I don't know how anyone got anything accomplished even ten years ago." 

Talia laughs as they start to walk downstairs. Derek stands up, wolf pushing him toward Stiles, and moves just in time to see Stiles preceding his mother down the steps. He opens his mouth, tries to draw in any scent from Stiles, but can't. It has to be magic -- but hunters don't use magic, they're more likely to kill a magic-user than to work with one. Maybe this is the difference between a hunter and what Peter called him, a Shadowhunter. 

Stiles pauses when he sees Derek, gives Derek a smile and an acknowledging nod, and Derek preens at the recognition, his wolf letting out a pleased rumble at the sight of their mate meeting their eyes and glad to see them. 

...Wait. _Mate_? There's no way; Derek hasn't even _scented_ the man, and he's a _man_, a man Derek's only laid eyes on this once, a man who's -- leaving. He's leaving, Stiles is leaving, he can't _leave_. 

Derek runs to the door, nearly collides into his mother. Stiles looks at him with concern and something that Derek hopes is curiosity, asks, "Is everything all right, Beta Hale?" 

"My son," Talia says. "Derek." 

"You can't go," Derek says, panicked and flustered and stumbling over his words. "You can't leave, you can't just -- I have to -- your _scent_, what is it, and what are you, and when are you -- will you come back, you can't just _go_, not without -- _please_, I --" 

Talia's hand curves around Derek's neck and squeezes; Derek whines, tilting his head back and showing off his throat to his alpha and his mate. "Are you saying what I think you're saying, Derek?" Talia asks. "Are you _sure_?" 

Derek wriggles his way out of his mother's hold and snaps his teeth at her. She lets her eyes flood alpha red and while a small part of Derek wants to whine and display his throat and belly, the larger part's in control; he gets between his alpha and his mate and snarls at the threat, teeth bared and ready to bite. 

A hand, then, on Derek's shoulder, another on his hip, a nose that draws a cold line from the pulsepoint in Derek's throat up to the soft skin behind his ear. "Calm, pup," his mate says. 

Derek lets out a disapproving rumble at the pet name but gradually wrestles the wolf under control, using the anchor of his mate's body pressed tight to his. When his mind's clear, he flushes as he meets his mother's gaze, opens his mouth to apologise but closes it before he can find the words to explain. 

"Alpha Hale," Stiles says, "would you excuse us for just a moment?" 

Talia studies Derek, eyes flicking once to Stiles, gaze taking in the way Stiles is practically wrapped around Derek and how much Derek's relaxed into the hold when Derek doesn't even care for pack touches all that much. "Just a moment," she agrees. 

Stiles unwinds himself from Derek; when Derek realises, he turns in a panic, but Stiles merely holds out one hand. Derek takes it, flushing, and lets Stiles pull him outside, off to the edge of the trees, close enough for Talia to see but, if she's being polite, not hear. 

"You want my scent, Derek?" Stiles asks. "Once you know, you can't unknow. My keeping it hidden among your pack is good manners, not distrust." 

"Please," Derek says. 

Stiles nods, grabs hold of the pen-thing Derek noticed earlier, and lifts his shirt. There's a tattoo on his right hip, thick, dark lines in a pattern Derek doesn't recognise. Stiles puts the tip of the pen to one side of the tattoo and draws a line straight through it. For a moment, the scent of heat and pain fills Derek's nose, but a moment later -- 

Ozone. Mountain air and thick forest, dark skies and lightning, feathers and blood, so much blood, all bound up in something Derek's never smelled before but could only describe as _power_. 

"I --," he breathes, eyes wide as he opens his mouth so the scent hits the back of his throat. Stiles shifts backwards, looks and smells -- under everything -- hesitant, worried. Derek shakes his head, follows Stiles and, when he's close enough, faceplants into Stiles' neck, taking in ragged, greedy inhales large enough to leave him lightheaded. 

"Oh," Stile says, quiet, as he lifts one hand to Derek's neck, fingertips running through the short hair just above Derek's nape. "Are you -- really?"

Derek's dizzy and overcome, that's the only reason he can think of for what he does next. He snuffles, licks Stiles' skin, tastes salt and warmth and _flesh_. There's a steady rumbling purr coming from his chest and when Stiles' hand goes upward, when Stiles gently, tentatively curls long, slender fingers in Derek's hair, anyone would forgive Derek for opening his mouth and _biting_.

Fangs buried deep in the meat of Stiles' shoulder, Derek hears his mother's furious shout coming from behind him. He doesn't care, though, not when Stiles' blood is trickling into his mouth and down his throat, not when Stiles is pulling Derek's hair tight, not when Stiles' heart is racing and his body's pressed to Derek's, not when Derek can feel how hard Stiles is and smell how much Stiles _wants_ this, wants _him_. 

"Mine," Derek growls, word coming out garbled around the bite of flesh in his mouth. "_Mine_." He feels another 'wolf approaching and reluctantly lets go of his mate's skin, licking his fangs and his lips before turning around and snap-snarling at the intruder. The other 'wolf growls and Derek _roars_, dropping to a crouch. The beta shift comes over him quick, fluid and flawless, but it doesn't stop at his face and hands. It keeps going, down his spine and to his feet, up through his legs and belly and throat, and then Derek roars again but the noise is all wolf, pure wolf, four-legged and furious wolf. 

"Derek," the other 'wolf says. "Derek, you're --" 

Derek's going to leap, attack, defend his mate and punish the interloper for interrupting them, but then his mate's fingers run through his scruff, legs pressing against his flank. "Derek, patience," his mate says. 

The wolf grumbles but settles, pressing back against his mate, head turning to lick at his mate's fingers, content to ignore the other 'wolf in the face of how calm and content his mate smells. 

"I didn't know he was going to do that," the other -- 'wolf? person-shaped 'wolf? says. "I'm sorry, Stiles." 

"Don't be, Alpha Hale," Derek's mate says. "If anyone should be apologising, it's me. I seem to have stolen your son and inserted myself into your pack in one fell swoop." 

A cacophony of smells fills the air, so much that Derek sneezes once, twice, and, on the third sneeze, finds himself sitting on the ground, naked and sore and utterly confused. 

Stiles weaves his fingers through Derek's hair, nails scritching at Derek's scalp. Derek hums, leans against the steadiness that Stiles offers and feels his eyes go heavy-lidded. 

Talia sighs, says, "I don't want him anywhere near the 'wolves in Seattle, but you need to stay together to stabilise the bond while it's still fresh." 

"I'll make some calls," Stiles says. "Someone else can deal with it. The Clave owes me, anyway, and there's still some pity I can use to my advantage." He pauses, says, carefully, "I'd like to take him with me, Alpha Hale. For a week or so, back to my home, so we can get used to each other and figure out what we're going to do." 

"Not Alicante," Talia says, delicately asking half a question. 

Stiles lets out a noise that Derek _thinks_ might be a laugh. "Not Alicante," he says. "After my parents -- well. I couldn't live there anymore. No, I have a home in Brocelind Forest."

Forest -- that might explain part of Stiles' scent, the one that speaks of fresh growth and warm dirt, the earthy hint buried amidst the magic and power and feathers and the cold, crisp air of mountains. 

Talia gives Stiles a steady, even look, then looks down at Derek. "Go and pack for a week," she says. "Clothes, books, take your homework and try to work ahead. I'll call the school." 

Derek stands up, says, "I'll be right back. You'll --," and he trails off, feels stupid for asking, stupid and unsteady and so very young compared to his mother and his mate. 

"I'll wait right here," Stiles says. "I won't leave without you, don't worry." 

Grinning, Derek leans over and licks Stiles' jaw before jogging back to the house. His wolf's yipping and spinning in circles, his own heart's racing. He leaps up the porch steps, gets to the door and looks back, only to see Stiles standing there, looking at him, waiting for him, smiling at him. 

Derek throws his head back and howls in celebration.


End file.
